console 命令行工具 X clear

console

<div class="box">
  <div class="center"></div>
</div>

.box {
  background-color: #ccc;
  height: 200px;//必须
}
.center {
  margin: 0 auto;
  width: 100px;
  height: 100px;
  transform: translateY(50%);
  background-color: #fff;
}